Yanmar Service in Long Beach Area
First try S & W Diesel in Wilmington. (310) 835-3155, Don Peters is the owner. They are authorized Yanmar and Perkins service and distributors. Don did the top end rebuild on my 1GM10.
Or try RS Marine in San Pedro at (310) 547-9951. These guys are also Yanmar authorized service and distributors but the owner is partially retired and I think they are only open about 4 days a week from 7:30am to 3pm.
Good Luck, Both companies take a long time to get the work done. Good work though.